Effects of enteric-coated, low-dose aspirin on parameters of platelet function

Background: Aspirin is widely used as an anti-thrombotic drug; however, it has been suggested that enteric-coated formulations of aspirin may be less bioavailable and less effective as anti-thrombotic agents. Aim: To assess the effect of a formulation of enteric-coated, low-dose (81 mg) aspirin on serum generated thromboxane B-2 and platelet aggregation in healthy subjects. Methods: Twenty-four subjects participated in a double-blind, randomized, placebo-controlled, parallel-group, multiple-dose study. Twelve subjects in each of two groups received a daily oral dose of enteric-coated aspirin (81 mg) or matching placebo for 7 days. Serum thromboxane B-2 and platelet aggregation (using 1 mM arachidonic acid and 1 mug/mL collagen as agonists) were measured 1-3 days prior to day 1, on day 1 (prior to therapy) and 4 h after the last dose on day 7. Results: After seven daily doses of enteric-coated aspirin, the mean percentage inhibition from baseline of ex vivo generated serum thromboxane B(2)was 97.4%, compared with a 7.8% increase after placebo treatment. The mean percentage inhibition of arachidonic acid- and collagen-induced platelet aggregation was 97.9% and 70.9%, respectively, following enteric-coated aspirin, compared with -1.0% and 2.7%, respectively, after placebo. Conclusions: The anti-platelet effects of multiple, daily, low-dose aspirin (as assessed by inhibition of serum thromboxane B-2 and platelet aggregation) are not adversely affected by enteric coating.